Autoclaves for sterilizing instruments, for example, dental and surgical instruments, have been used for decades. Of particular interest are freestanding, self-contained autoclave units similar to that illustrated in FIG. 10. The prior art autoclave or sterilizer 20 includes a sterilizing chamber 22 surrounded by heaters, for example, band heaters (not shown). Upon placing the items to be sterilized in the chamber 22, a user, via a control panel (not shown), initiates a sterilizing cycle the first step of which is to use the heaters to heat the sterilizing chamber to a temperature, for example, 275.degree. F. Upon reaching that temperature, the user is signaled to turn the knob 26 which operates a valve 28, sometimes referred to as a metering valve, thereby causing a known quantity of sterilizing fluid, for example, water or sterilizing chemicals, to flow from a shotwell 30 through tubing 32 into the chamber 22. The sterilizing fluid immediately vaporizes, thereby producing a sterilizing steam or vapor which creates a vapor pressure of 20-40 pounds per square inch.
At the end of a sterilizing cycle, the operator is signaled to return the control knob 26 to its original position, and the valve 28 permits the sterilizing chamber 22 to be purged by a vacuum or pressurized air through a controlled vent system. Thus, the valve 28 functions as a two-way valve. The pressurized air is supplied to a purge inlet (not shown) of the sterilizing chamber 22 and forces the vapor from the sterilizing chamber 22, through the tubing 32, through the valve 28, through a vent line 36 and into a condensing manifold 38. The purged sterilizing vapors and fluid then pass through condensing and cooling coils 40 and into a waste tank 42. The waste tank is vented via tubing 44 through a carbon filter 46 to atmosphere. The manifold 38, coils 40, waste tank 40 and filter 46 function together to form a controlled vent system in which the used sterilizing fluid and vapors are contained and processed so that waste materials are collected and clean air is discharged into the environment. The specific structure of a controller vent system will vary depending on the sterilizer, the sterilizing fluid, the items being sterilized and other factors. A sterilizer providing the sterilizing cycle just described is commercially available as a Chemiclave EC5500/EC6000 from Bamstead.vertline.Thermolyne Corporation of Dubuque, Iowa.
Of interest to the present invention is one known valve 28 which is shown as partially disassembled in FIG. 11. The valve 28 has a shotwell 50 which is fluidly connected to a valve stem 52 that includes various passages 54 that are operatively coupled to passages within a valve body 56, thereby interconnecting ports 58 in the appropriate manner to achieve the desired two-way valving action. A valve of the construction shown in FIG. 11 has proven to have certain disadvantages. For example, the tapered sides 53 of the valve stem 52 must be machined to perfectly match the tapered sides 60 of a bore within the valve body 56. The mating of the tapered sides 53 with the tapered sides 60 must provide a tight seal against the fluids and pressurized vapors passing through the valve 28. Therefore, the tapered sides 53, 60 must have very accurate manufacturing tolerances so that such a seal is achieved. Further, the tapered sides 53 on the valve stem 52 are also coated with a "TEFLON" material which is machined to provide the final taper to the desired accuracy. The valve body 56 is normally nickel plated to provide the desired hardness. The processes of applying the "TEFLON" coating and nickel plating are expensive and if not properly performed, can contribute to a malfunction of the valve 28. The net result is that valves of such a design are difficult to manufacture and sometimes fail after a relatively short period of time.
The valve 28 provides only a single position of the valve body 56 with respect to the valve stem 52 at which the shotwell 50 is purged of any excessive pressurized sterilizing fluid and/or vapors. In that position, the vent holes 62 of the valve body 56 are aligned with the vent holes 54, thereby purging pressurized vapors from the shotwell 50 directly into the atmosphere and bypassing the controlled vent system within the sterilizer used to vent the chamber 22. With this valve construction, the shotwell is normally vented to atmosphere within the sterilizer housing. As will be appreciated, venting pressurized vapors within the sterilizer housing has several disadvantages. First, the vapors and fluid are hot and under pressure which results in such vapors and/or fluid being projected from the holes 62 into the housing of the sterilizer. Such spitting action of the sterilizing fluid and/or vapors is unpredictable. Not only is it undesirable to have an uncontained liquid within the sterilizer housing, but such vented vapors and liquid may present an undesirable odor, possibly facilitate corrosion and in some applications be volatile.
Another known valve 28 is shown partially disassembled in FIG. 12. Valve components in FIG. 12 that are common with those described earlier with respect to FIG. 11 are commonly numbered. The valve stem 52 has a straight cylindrical side 57, and slides into a cylindrical bore 59 within the valve body 56. O-rings 61 are used to seal the valve stem 52 within the cylindrical bore 59, and an O-ring 63 is used to seal the fluid connection between each of the passages 54 within the valve stem and passages (not shown) intersecting the bore 59 within the valve body 56. While this design eliminates the problems associated with the tapered design of FIG. 11, the design of FIG. 12 is not trouble-free. The O-rings 63 often swell from their contact with the fluid and steam within the sterilizer, thereby making the valve stem difficult to turn by hand. Further, during rotation of the valve stem 52 within the valve body 56, as one of the compressed O-rings 63 passes over a leading edge of the passage openings within the bore 59 of the valve body 56, a portion of that O-ring 63 expands slightly into the valve body passage openings. Upon further rotation of the valve stem 52, that expanded portion of the O-ring 63 must pass over the trailing edge of the valve body passage opening and recompress. That action causes severe wear on the O-ring 63; and over time, the useful life of the O-ring 63 is significantly shortened. The valve 28 illustrated in FIG. 12 vents the shotwell 50 through holes 62, and thus, has the same disadvantages in that regard as previously discussed with respect to the valve illustrated in FIG. 11.
A further known valve 28 is shown partially disassembled in FIG. 13. Valve components in FIG. 13 that are common with those described above with respect to FIGS. 11 and 12 are commonly numbered. The valve stem 52 has a curved surface 65, and slides into a cylindrical bore 59 within the valve body 56. O-rings 61 are used to seal the valve stem 52 within the cylindrical bore 59. An annular rubber seal 69 extends through a sidewall of the valve body 56, and has a curved end 71 that matches the curve of the surface 65. The sterilizer valve illustrated in FIG. 13 has essentially the same problems as the sterilizer valve illustrated in FIG. 12.
Thus, there is a need for a sterilizer having an improved valve that provides more reliable long term operation.